The prstat -L tool tells you the amount of CPU being used for each thread. If you collect a process stack using the pstack utility at the same time you run the prstat tool, you can then use the pstack output to see what the thread was doing when it had trouble. If you run the prstat and pstack simultaneously several times, then you can see over time if the same thread was causing the problem and if it was encountering the problem during the same function call. If you are experiencing a performance drop, then run the commands simultaneously every 2 seconds. If you are experiencing a passive or active hang, run the commands with a slightly longer delay, for example every 10 seconds or so.